Biodegradability Enhancement of 2,4-Dichlorophenol Aqueous Solution by Means of Photo-Fenton Reaction

Abstract

The degradation and biodegradability improvement of 100 mg · L⁻¹ solution of 2,4-dichlorophenol (2,4-DCP) has been investigated using the photo-Fenton reaction. The influence of reagents concentrations [H2O2 and Fe(II)], initial solution pH, as well as temperature were systematically studied. BOD5, BOD5/COD, BOD5/TOC, and COD/TOC ratios and the average oxidation state are presented. Concentrations of H2O2 and Fe(II), that gave total removal in 2.4-dichlorophenol and increase biodegradability, was determined. The treated solution toxicity was also evaluated. The biodegradability was measured as the BOD5/COD ratio was increased from 0 of the original solution to 0.3 at the point where all 2,4-DCP was removed from the solution. This was combined to increase the average oxidation state from −0.4 up to 1.35. The temperature shows a good effect in the removal rate but a small effect in biodegradability enhancement. The general trend indicates that the degradation efficiency of the photo-Fenton process is related to the initial solution pH, with better efficiency achieved at acidic pH (pH ≈ 3). The oxidation reaction was successfully modeled to pseudo first-order kinetic. The apparent rate constant was found to be dependent on initial hydrogen peroxide concentration, operational temperature, and initial solution pH. As the initial concentration of H2O2 was increased from 15 to 50 mg · L⁻¹, initial Fe(II) concentration was fixed to 10 mg/L, the pseudo firstorder rate constant was increased from 1.2 h⁻¹ to 3.42 h⁻¹. The photo-Fenton process is known to be an expensive treatment option due to the use of expensive reagents. For process economizing, the effect of the iron catalysis recycling on the degradation efficiency was tested. Significant 2,4- dichlorophenol degradation efficiency was achieved by iron recycling for three times; 77% of 2,4- DCP degradation was achieved for the first recycling, 55% for the second recycling, and 40% for the third recycling.